power measurement of system_off app on nRF54-DK

[bios-bob]

i've captured the following using a joulescope js-220 as an inline current meter across the VDDM CURRENT MEASURE jumper on my rRF54-DK board....

i'm running the system_off sample app, with the GRTC configured for a 2Hz wakeup....

per instructions in the docs, i don't have any open serial ports or attached debuggers....

now, take a look at the 85uJ consumed in the pink region -- consistent with an active system....

what i can't explain, however, is the 69uJ consumed in the green region -- which subsumes the pink region....

indeed, the blue region reports -8uJ over an interval when the system is off....

is there an explanation for what otherwise seems too good to be true ???

[Simonr]

Hi

So, this could be the capacitor on DECD that's charging up. Here's a plot from the power profiler kit waking up and advertising once before going to sleep again, as I assume your device is also waking up here and turning off again.

When the nRF54L wakes up,the DECD capacitor is being charged from 0.7V to 0.9V so you get an inrush current on it. The same amount of energy will be saved after the event when it goes back down to 0.7V, so I think what you're seeing could be realistic without going into the nitty gritties. 

Best regards,

Simon

[bios-bob]

i switched to the button-press version of `system_off`, and simply let the board sit in SYSTEM_OFF indefinitely....  measuring current now, everything stayed flat at -6uA....

assuming i'm consistent with this configuration from the user's guide:

will i ever see this number on my nrf54-DK???  

[Simonr]

Hi

Some leakage will likely be there on the DK, but you should be able to get lower than 6µA in system OFF mode. We've been able to see down to 3µA on a DK in System ON idle mode. What version of the nRF54L15 DK are you using on your end, and what NCS version do you use for the projects. Finally, how exactly are you measuring the current consumption on the DK, are you following the current measurements section of the DK user guide? 

Best regards,

Simon

[bios-bob]

just to be clear, i'm seeing -6 uA in system OFF -- that's a negative number!!!!  one of the capacitors is apparently acting as an energy harvester ;-)

i just received the DK a week ago; the sticker on the board has a 0.9.2 version number....

i'm measuring with a joulescope j220, with the "high-side" of the meter connected to the left-pin of P6 and the "low-side" to the middle-pin...

could i simply supply 3V3 to the MCU (unplugging the USB) and measure power consumption here????  or are there way too many peripherals on the board that would be included in the measurements????

[Simonr]

I see, I thought you just mean 6µA there. If it's a negative number something is definitely off with the current measurement here. I'm not familiar with this joulescope, but how accurate is it supposed to be? You should also be able to supply the MCU using P6 as well as that's how we generally measure with using the PPK2 (using it as a source meter). Supplying the board from J3 will lead to a lot of leakages and other devices being powered as well.

The description of how you measure seems correct, but I guess it depends on how the board is powered in this case. There seems to be some leakage resulting in this negative current somewhere. 

Best regards,

Simon